Most modern cities are battling with increasing amount of garbage/waste generated and accumulated on a daily basis. Effective ways of managing the waste has become indispensable for maintaining sanitation and general quality of urban life. Sustainable and innovative solutions for managing waste are a critical need.
There are various modes of waste disposal known to us such as landfills, incineration, recycling, biological reprocessing etc. The most acceptable and sustainable modes of waste management are recycling and reprocessing for resource and energy recovery. In recycling, materials generally undergo a chemical transformation and resultant products are recycled to be used for various purposes. For the purpose of resource recovery the organic waste is preferably anaerobically digested (also called Anaerobic Composting or Biomethanation) as compared to aerobic digestion to obtain compost which can be used as an organic fertilizer on agricultural fields. Anaerobic digestion of organic waste results in energy in the form of biogas, and compost in the form of a liquid residual. The biogas consists of methane and carbon dioxide and can be used as fuel or, by using a generator, it can be converted to electricity on-site. This reduces greenhouse gas emissions by using methane as an energy source which would otherwise be emitted from landfilling waste. Landfilling waste gas is similar in composition to biogas with lower amount of methane and differences in component gases. However, the conversion of biogas to electricity is not economically attractive and also results in significant loss of energy during conversion.
Methane, present in biogas or landfill gas, can also be converted to syngas and then to chemicals such as methanol. This gas to liquid conversion, however, happens at high temperature and pressure necessitating huge capital investments. Efficient utilization of biogas as well as methane has always been a challenging task.
Advances in biotechnology are enabling development of new and improved microorganisms for efficient degradation of biomass. However, the existing state of the art does not provide for a unified and efficient way of converting organic wastes and more specifically biogas or methane to target chemicals by employing recombinant microorganisms.